While cage-free or free-range egg production systems may have advantages for individual chickens, they may not be best for the environment or people, according to a recent article in The Guardian.

“There are a lot of misconceptions around free-range,” says Frank Mitloehner, a UC Davis animal science professor and livestock air quality specialist.

Cages make it easier to extract eggs, which roll into a collection area. These systems also remove manure that falls through the cage bottom onto a conveyor belt. In a cage-free system, the manure stays in the barn and can build up.

“Animals have a natural drive to work their way through manure to find worms, insects and so on, and they do eat manure as well,” Mitloehner says. “So that’s a big problem with respect to food safety and animal safety because animals in that system are now in contact with their manure.”

Cage-free systems also pose health risks. “I’m looking primarily at air pollutants and I’ve found that in those systems with manure inside that is not being taken out frequently, manure that builds up causes large amounts of dust particles and those particles contain pathogens and toxins that people and animals then inhale,” he said.

(Read the full story by Amy Westervelt, March 7, 2014 in The Guardian.)

Update: Mitloehner was not part of a study referred to in The Guardian article. However, he was an investigator on another study presented to the Poultry Science Association on the social sustainability of egg production. It examined current knowledge of the environmental impacts of egg production systems and identified topics requiring further research. View an in press version of the Poultry Science journal article, “Environmental impacts and sustainability of egg production systems.”